1. Field of the Invention
The present invention relates to a method for fabricating an alumina, and more particularly, a method for fabricating a high specific surface area mesoporous alumina.
2. Description of the Related Art
According to pore sizes, porous materials are generally classified into microporous materials with a pore size less than 2 nm, mesoporous materials with a pore size between 2 nm and 50 nm, and macroporous materials with a pore size more than 50 nm. However, because the pore diameters of microporous materials are too small and the pores of macroporous materials are not uniformly distributed, mesoporous materials without the above defects are widely used as catalysts, carriers for catalysts, gas adsorptive agents, filter materials, etc. Among the mesoporous materials, mesoporous alumina is easy to obtain and quite cheap so that it is used a great deal. Besides, with the greater needs for specialty chemicals, mesoporous alumina is highly profitable as a high unit priced fine-purification, adsorptive material.
The conventional method for manufacturing a mesoporous alumina is mainly divided by starting material into a more expensive group of aluminum alkoxide and a cheaper group of aluminum salts such as aluminum nitrate and aluminum sulfate. Taking aluminum alkoxide as a starting material, the method for fabricating a mesoporous alumina can produce a porous alumina with its porous diameter maintained on 11 nm. However, the cost of aluminum alkoxide is high, and its specific surface area would be less than 150 m2/g when sintering at 1030° C. with the result that it would be limited in practice.
Comparing with aluminum alkoxide, taking the aluminum salts, such as aluminum nitrate, aluminum sulfate, aluminum chloride and sodium aluminate, as the starting material could lower the material cost, but the mesoporous alumina obtained by the conventional method has many defects in its porous characteristics. For example, the distribution of the pores is too wide to apply to a fine-purification system that requires high operating demands; the temperature for sintering is too low to use in petroleum cracking; the pore volume is too small, etc. Although the conventional method could overcome the above limitations by adding a PEO surfactant as a structure directing material, the pore volume of its mesoporous product is still too small.